GB2205394A - Monitoring of tool operations - Google Patents

Abstract

In situations where a tool, such as a laser-carrying tool, is under programmed robotic control, the set working pattern of the tool is arranged to be within the field of view 14 of a radiation sensor but the field of view is masked at 16 either physically or electrically such that tool movements within the masked zone are acceptable but movements beyond this zone give rise to signals to enable remedial action to be taken to protect personnel in the vicinity of the tool. The sensor may be responsive to the laser beam radiation or to another radiation source carried by the tool. Welding and cutting are mentioned. Human body radiation may also be detected. <IMAGE>

Description

Monitoring of Tool Operations This invention relates to the monitoring of tool operations especially in circumstances where the tool forms, for example a laser tool, part of a programmable robotic unit enabling the tool to be manipulated in accordance with a preprogrammed pattern of working movements.

High power lasers are now available for performing operations such as welding and cutting. Such lasers are extremely hazardous to personnel and can lead to irreversible tissue damage. It is therefore important that lasers should be operated in such a way that personnel are safeguarded from possible laser exposure.

Where lasers are used in conjunction with robotic equipment, the equipment can be programmed so that the laser beam follows a well-defined set of working patterns in repeatedly executing a particular sequence of operations involving for example welding or cutting of identical workpieces and this, to a degree, is advantageous from the safety standpoint provided that the laser tool does not deviate from the programmed pattern of movement. In practice, this ideal cannot be guaranteed; for example erratic operation of the robot may occur with the risk of the laser tool being moved into a position where the laser beam poses a hazard to personnel in the vicinity.

The object of the present invention is to provide a system for detecting deviation of a tool from a set pattern of working movements.

According to one aspect of the invention a system for monitoring movement of a tool comprises: at least one radiation sensor device having a field of view which encompasses a set pattern of working movements of the tool, means for directly or indirectly masking the field of view of the or each sensor device to define an effective field of view into which a radiation source associated with the tool should not encroach when the latter executes said set pattern of working movements; and means for producing a safeguard-initiating signal in response to detection of the radiation source by the sensor device or at least one of the sensor devices.

According to a second aspect of the invention a system for detecting deviation of a tool from a set pattern of working movements comprises: at least one sensor device responsive to a radiation source associated with the tool (which radiation source may be constituted by a laser beam forming part of the tool or by an alternative radiation source), the or each sensor device having a field of view which encompasses said set pattern of working movements, as seen from the viewing direction of the sensor device; means for directly or indirectly masking the field of view of the or each sensor device to restrict its effective field of view to outlying zones beyond the zone in which said radiation source is viewable while the tool executes said set pattern of working movements; and means for producing a safeguard-initiating signal in the event that the radiation source is detected within said effective field of view of the sensor device or any one of the sensor devices.

Preferably at least two sensor devices are provided for viewing the tool from at least two different angles, whereby the sensor devices collectively simulate three dimensional viewing of the tool as it executes said set pattern of working movements.

Where an alternative radiation source is employed it may comprise for instance a light emitting source mounted on the operating head of the tool. Where the sensor device is responsive to radiation emitted by a laser beam, the device may be an infra-red sensor, eg. one employing infra-red sensitive cadmium mercury telluride and lead tin telluride materials.

The masking of the field of view of the or each sensor device may be achieved directly by a mechanical masking arrangement which may be interposed between the sensor device and the tool. Alternatively, masking may be effected indirectly by electrical or electronic means in such a way that output signals produced by the or each sensor device as a result of said radiation being incident on a predetermined zone or zones of the sensor device are for example suppressed or categorised as acceptable whereas those sensor output signals produced as result of the incidence of said radiation on the sensor device but outside said preselected zone or zones are used to operate said safeguard-initiating signal-producing means.

In the latter case, means may be provided for identifying the output signals produced by the or each sensor device with the particular zones of the sensor device from which they originate and masking data may be stored electrically for comparison with identified origins of the output signals whereby they can be classified as acceptable (if originating from said preselected zone or zones) or unacceptable. For instance, the or each sensor device may comprise an array of radiation-sensitive elements so that the output signals can be identified with a particular element and electronic store means may store data indicating which elements may or may not produce acceptable output signals.

The data stored may be varied with deliberate changes in the set pattern of working movements of the tool. Where a mechanical masking arrangement is employed, the physical form of the mask may be varied in such circumstances, eg. by substituting masking components which define differing masked areas corresponding to different set patterns of working movements.

The safeguard-initiating means may be operable to modify operation of the tool - for example in the case of a laser tool by disabling the laser or interrupting the laser beam (for instance, by means of a shutter device) or by moving the laser tool to a safe position.

In a preferred embodiment of the invention the tool forms part of programmable robotic apparatus incorporating a computer whereby the robot mechanism can be preprogrammed to move the tool through the set pattern of working movements. In general, the working movements will take place in three dimensions whereas each sensor device will effectively have a two dimensional field of view. The computer is therefore conveniently arranged to translate the three dimensional movement of the tool into at least one two dimensional representation of the field of view circumscribing all movements of the radiation source as viewed from at least one direction.Thus, for example, where three sensor devices are employed at different viewing angles to provide all-round viewing of the tool, the computer may be arranged to produce three such two dimensional representations each corresponding to respective viewing angles of the sensor devices. It will be understood that each such representation will define the masking area for the respective sensor device and the representation may, in turn, be implemented for example by a mechanical masking arrangement or by electrical or electronic means.

If desired, the safeguard-initiating means may be arranged to produce a signal only when the radiation source is incident on the effective field of view or part thereof for a period of time exceeding a threshold value.

Thus, a momentary glimpse of the radiation source within the effective field of view may not require modification of tool operation since, in the case of a laser tool for example the risk of momentary exposure may not constitute a health hazard where a relatively low power laser beam is used. On the other hand, sustained incidence of the radiation source on the effective field of view may lead to a health hazard even where relatively low power laser beams are used.

To promote further understanding of the invention, reference is now made to the accompanying drawings, in which: Figure 1 is a schematic view illustrating a set pattern of working movements followed by a preprogrammed robotically manipulated laser tool; Figure 2 is a schematic view of the field of view of a sensor device, as modified by a masking element.

In Figure 1, the complex series of lines represents a set pattern of working movements followed by laser tool in performing a programmed sequence of operations, eg.

spot welding operations, the laser tool being mounted on a computer controlled robotic mechanism (not shown).

Although these movements, commencing and terminating at point 10, are depicted in two dimensions in the drawing, it will be appreciated that such movement will generally have components in directions normal to the plane of the paper, ie. in three dimensions. As viewed perpendicularly with respect to the plane of the paper, these movements are circumscribed by the boundary depicted by phantom line 12. However, when viewed from a different angle, the circumscribing boundary will generally be of a different shape.

While the laser tool executes the programmed pattern of working movements, personnel in the vicinity can be safguarded since suitable precautions can be taken to ensure that they are shielded when the laser beam is following its programmed pattern of movements. However, any departure from the programmed pattern due to, for example, erratic robotic operation may pose a serious health hazard.

In accordance with the invention, the working movements of the laser tool are viewed by at least one radiation sensor arranged to respond to radiation emitted by the laser beam per se or by a radiation source, such as a chemical radiation or light-emitting source, mounted on the working head of the tool. Typically, there will be at least three such sensor devices each disposed to view the tool from a different angle, ie. so that an all-round view is obtained. In Figure 2, the circle 14 represents the overall field of view of one of the sensor devices, as defined for example by an object lens forming part of an optical system associated with the device.

Part of this overall field of view is masked by a masking element 16 whose boundary is such that it circumscribes the pattern of working movements of the tool as viewed from the angle at which the sensor is disposed. Thus, in Figure 2, the masking element 16 correponds to the boundary 12 in Figure 1 if the sensor device views the working movements perpendicularly to the plane of the paper.

In this way, the sensor device has its effective field of view limited to the regions outlying the masked zone 16 and with the robotic mechanism operating correctly, the radition source of the laser tool should not encroach on the effective field of view of the sensor device. If the radiation source does encroach on this restricted field of view, the sensor device will respond and produce an output signal which may be utilised to modify operation of the laser tool, as previously described. Thus, the masks associated with the sensor devices collectively define a three dimensional envelope outside which the laser tool radiation source should not normally be detectable.

Although the illustrated embodiment relates to the case where physical masking is employed, as described hereinbefore the masking may be achieved indirectly by differentiating between the output signals of the sensor devices according to whether or not such signals stem from incidence of radition on selected zones of the radiation sensitive elements or area of the sensor device.

If desired, the sensor device(s) may be arranged so as to respond not only to encroachment of the laser tool on the unmasked field of view but also the entry of personnel into its viewing field, eg. the sensor may detect the thermal radiation emitted by personnel. Such an arrangement allows remedial action to be taken if a person approaches too closely to the tool with consequent danger to health.

Although the invention is described with particular reference to a robotically-controlled laser tool, the tool may be of some other form, eg. one carrying a cutting torch. In addition, the sensor device may be masked in such a way that it can monitor more than one tool simultaneously.

Claims (13)

Claims

1. A system for monitoring movement of a tool comprises: at least one radiation sensor device having a field of view which encompasses a set pattern of working movements of the tool, means for directly or indirectly masking the field of view of the or each sensor device to define an effective field of view into which a radiation source associated with the tool should not encroach when the latter executes said set pattern of working movements; and means for producing a safeguard-initiating signal in response to detection of the radiation source by the sensor device or at least one of the sensor devices.

2. A system for detecting deviation of a tool from a set pattern of working movements comprises: at least one sensor device responsive to a radiation source associated with the tool, the or each sensor device having a field of view which encompasses said set pattern of working movements, as seen from the viewing direction of the sensor device; means for directly or indirectly masking the field of view of the or each sensor device to restrict its effective field of view to outlying zones beyond the zone in which said radiation source is viewable while the tool executes said set pattern of working movements; and means for producing a safeguard-initiating signal in the event that the radiation source is detected within said effective field of view of the sensor device or any one of the sensor devices.

3. A system as claimed in Claim 1 or 2 in which at least two sensor devices are provided for viewing the tool from at least two different angles, whereby the sensor devices collectively simulate three dimensional viewing of the tool as it executes said set pattern of working movements.

4. A system as claimed in Claim 1, 2 or 3 in which the radiation source comprises a light emitting source mounted on the operating head of the tool.

5. A system as claimed in any one of Claims 1 to 4 in which the masking means comprises a mechanical masking arrangement which may be interposed between the sensor device and the tool.

6. A system as claimed in any one of Claims 1 to 4 in which masking is effected indirectly by electrical or electronic means in such a way that output signals produced by the or each sensor device as a result of said radiation being incident on a predetermined zone or zones of the sensor device are suppressed or categorised as acceptable whereas those sensor output signals produced as result of the incidence of said radiation on the sensor device but outside said preselected zone or zones are used to operate said safeguard-initiating signal-producing means.

7. A system as claimed in Claim 6 including means for identifying the output signals produced by the or each sensor device with the particular zones of the sensor device from which they originate and masking data is stored electrically for comparison with identified origins of the output signals whereby they can be classified as acceptable (if originating from said preselected zone or zones) or unacceptable.

8. A system as claimed in Claim 5 or 6 in which the or each sensor device may comprise an array of radiation-sensitive elements so that the output signals can be identified with a particular element and electronic store means stores data indicating which elements may or may not produce acceptable output signals.

9. A system as claimed in any one of Claims 1 to 8 in which the safeguard-initiating means may be operable to modify operation of the laser tool by disabling the laser or interrupting the laser beam or by moving the laser tool to a safe position.

10. A system as claimed in any one of Claims 1 to 9 in which the tool forms part of programmable robotic apparatus incorporating a computer whereby the robot mechanism can be preprogrammed to move the tool through the set pattern of working movements.

11. A system as claimed in Claim 10 in which the computer is arranged to translate the three dimensional movement of the tool intQ at least one two dimensional representation of the field of view circumscribing all movements of the radiation source as viewed from at least one direction.

12. A system as claimed in any one of Claims 1 to 11 in which the safeguard-initiating means is arranged to produce a signal only when the radiation source is incident on the effective field of view or part thereof for a period of time exceeding a threshold value.

13. A system for monitoring movement of a tool substantially as hereinbefore described with reference to the accompanying drawings.